Seashells provide climate and archaeological data
Over their lifetime, marine molluscs build up a calcium carbonate shell, whose composition is influenced by the external environment. In turn, locked within the shell composition is highly detailed climate information. Archaeologists investigating shell debris from ancient settlements, known as shell middens can reconstruct past changes in climate and gain knowledge about the exploitation of coastal resources by human populations. Deposits of shells left over from human activities dating back over 160,000 years can be found around the globe. However, the vital information they contain is practically inaccessible due to a reliance on expensive and labour-intensive laboratory techniques. As funding and labour are usually scarce, current studies tend to have small and unrepresentative sample sizes, resulting in a lack of robustness and comparability between different sets of data. Laser analysis gives quick results The EU-funded Horizon 2020 project ACCELERATE addressed these challenges by developing a fast and practically free-of-cost technique for analysing climate records in shellfish remains. Scientists used laser-induced breakdown spectroscopy (LIBS) to retrieve information preserved in the elemental composition of carbonates within the shells of marine molluscs and established a standardised approach for applying this technique to coastal shell midden deposits. Coastal shell middens are widespread around the world and can be the size of a house or even several kilometers long, representing a huge potential climate archive, which scientists were previously unable to representatively access. “In addition to the climatic and ecological information from the shells themselves, the middens preserve archaeological artefacts and human burials extremely well because of the chemical environment the shell carbonate provides,” says researcher Dr Niklas Hausmann. LIBS utilises laser pulses to provide extremely rapid in situ chemical analysis, delivering data within split-seconds. “Knowing the result immediately rather than waiting a day or a week, means that you can quickly check your data and do the analysis again if necessary,” explains Dr Hausmann. “You can try out new sampling strategies and it’s a non-destructive technique, so you never run out of sample material.” Bigger sample, better results Speedy analysis allowed researchers to sample in two dimensions and fully map the shell record, making it possible to see data changes across all parts of the shell rather than just in a small area. “Overall, using maps increased the robustness of our interpretations enabling researchers to make sense of previously poorly understood climate records,” claims Dr Hausman. With larger datasets ACCELERATE also enables the analysis of how sub-annual shifts in the environment can have an impact on coastal wildlife by revealing seasonally extreme conditions more comprehensively. “A very hot summer, for example, can be enough to destroy large populations, but it would be invisible in an annual climate record. Furthermore, an increase in sample sizes means that we can look at climatic impacts on whole populations rather than only one animal. It is often the weaker animals that suffer the most, but are also overlooked by studies, whose sample size is restricted,” Dr Hausmann points out.
Keywords
ACCELERATE, shell, climate, midden, laser-induced breakdown spectroscopy (LIBS)
